The present invention deals broadly with the field of sound conditioning for the purpose of restricting the maximum sound pressure delivered to a hearer without sacrificing intelligibility. More specifically, however, the present invention deals with an acoustic conditioning system that is operational in modes both to effect sound attenuation and to accomplish amplification, as necessary. The focus of the preferred embodiment is a hearing aid which can be selectively switched between operational modes wherein high level sounds can be attenuated in normal, industrial or recreational environments, or amplified, as conditions warrant.
Noise protection is necessary in a multiplicity of circumstances. Absent some means for protecting against excessive noises, aggravated hearing problems could occur in a person of relatively unimpaired hearing. Various medical conditions exist, however, wherein a person""s hearing is particularly sensitive. One of these conditions is known as hyperacusis. Hyperacusis is a condition wherein a person experiences a collapsed tolerance to normal environmental sounds. It is a hearing disorder wherein the individual becomes highly sensitive to ambient noise. A person who experiences a condition such as hyperacusis loses much of his normal dynamic hearing range. Further, however, common noise conditions can be perceived as being unbearably loud. In aggravated conditions, the situation can be extremely painful.
A further hearing disorder of this nature is recruitment. In the case of hyperacusis, an individual is highly sensitive to sound but frequently experiences little or no hearing loss. A person with recruitment, on the other hand, is also highly sensitive to sound, but also experiences hearing loss. Extreme recruitment is a condition which is often confused with hyperacusis.
Obviously, there are other situations which dictate a need for aural protection. Persons having relatively normal hearing could experience conditions in loud industrial environments that could, over a period of time of exposure thereto, cause hearing impairment. Such loud environments may cause an aggravation of an existing hearing loss if aural protection is not used. In recognition of this fact, the Occupational Safety and Health Administration (OSHA) has imposed noise exposure limits for industrial environments. The standard noise exposure limit imposed is 90 dBA over an eight-hour period.
Another circumstance in which noise attenuation can be necessary is in vocational situations such as airport operations. Again, because of excessive noise, severe hearing impairment can result after exposure to such noise over time. Limitations are, therefore, imposed by governmental agencies in order to protect the hearing of employees working in such an environment.
Day-to-day military operations can also create conditions under which personnel experience extremely high noise levels. Obviously, a common military environment is air operations. Air operations are performed in virtually every branch of the armed services. In some cases, military personnel are exposed to helicopter noise; in other circumstances the excessive noise can be created by fixed-wing military aircraft. In either case, however, the noise level is far above a level to which personnel should normally be exposed.
Also in the military, personnel are exposed to excessive noise levels as a result of weapons firing. The weapons might be missiles, large guns, or small arms. In the case of virtually any weapon, however, high noise levels are generated which can cause damage to the hearing of personnel exposed to such noise.
Even apart from vocational and military environments, people are, on a day-to-day basis, exposed to loud noises, such as, for example, in recreational environments. Certainly, hunting is one environment in which a person is exposed to high decibel levels.
The problems of high noise level environments are aggravated by the fact that, very commonly, high level noise periods are alternated with other periods of time during which ambient noise is at a normal level. One very common solution offered to eliminate, or at least minimize, high noise level dangers is a device such as a common passive aural protector. Such a device typically includes a pair of cup-like structures which are mated together by a band which is fitted over a wearer""s head. The cup-like structures normally include some sort of padded material on an inwardly facing oval surface brought to bear against a side of the wearer""s head so that a cup-like structure tightly encircles the ear area of the individual. In the military, this type of device is known as xe2x80x9cMickey Mouse Earsxe2x80x9d, and it is a device which is totally passive in the way it functions. That is, it merely filters the noise in a passive sense.
Obviously other passive noise attenuation devices have been devised and are used in various environments. Another very unsophisticated system is common ear plugs.
Some sophisticated systems have also been created. For example, electronic earmuffs have been devised which serve to electronically filter noise to a tolerable level.
Most of such systems discussed above, however, merely function to attenuate noise. No relief is given, in systems which merely function to attenuate noise, for an environment wherein conditions vary between excessive noise, at one time, and normal ambient conditions, at another.
In the case of a person already having a hearing disability, noise attenuation means are necessary so as not to worsen such a hearing impairment during high noise level periods, but amplification means are necessary during normal ambient noise periods. Options available to individuals having such impairments, utilizing prior art technology, include wearing a normal amplification hearing aid without any type of acoustic protection. Such an option, however, places the individual at further risk to noise-induced hearing loss because hearing aids are not designed to hold down, to a sufficient degree, the maximum sound pressure delivered.
Other options include wearing some sort of passive hearing protection and no hearing aid. In such a circumstance, however, the individual would be limited or possibly even fully unable to communicate. He might, therefore, become disabled from performing work duties.
Electronic earmuffs, as previously discussed, serve to afford hearing protection to the user. They are, however, relatively clumsy as hearing aids for hearing impaired persons requiring amplification. The employment of a hearing aid underneath electronic earmuffs can result in acoustic feedback and resultant inability to pick up desired sounds.
It is to these problems and the dictates of the prior art that the present invention is directed. It is an improved acoustic conditioner which enables these problems to be significantly surmounted.
The present invention is a device which functions to condition acoustical energy brought to bear upon the ear of a user of the device. The device includes circuitry for implementing a mode of electronically attenuating excessive noise levels in the vicinity of the wearer while still amplifying speech, music and other desired sounds. Such attenuating circuitry includes components by which an output sound pressure level is compressed below a desired level.
In one embodiment of the invention, the device can further include components which effect implementation of a normal hearing aid amplification of ambient sound level mode so that a hearing impaired user of the device can hear in accordance with his needs. Certain embodiments of the invention also include structure to enable selective actuation of either the attenuation or amplification modes. A switch interposed in circuitry within a housing enclosing the various components of the device can be employed for this purpose.
The switch, in turn, can be controlled in a number of fashions. A manual toggle can be mounted on the housing and operationally connected to the switch so that the wearer of the device can volitionally and positively select between amplification and attenuation modes.
Automatic control means are also envisioned. Such automatic controls would function in response to the noise level which is sensed at the device. A resistor in the circuitry is used to implement noise protection. An automatic noise switch is utilized to short out or place the resistor into the circuit in response to the background noise level. Since, in most cases, speech, music and other desired sounds generate a relatively short-term signal and excessive noise generates a long-term stationary signal relative to the signal representative of desired sounds, differentiation of the two signals can be made by averaging the received signal over a long period of time. The present invention employs a rectifier to sense the long-term average signal level. A field effect transistor is employed as an analog switch in order to change the impedance across the resistor which is used to implement the noise protection mode.
The present invention is thus an improved acoustic conditioning device which solves many of the problems of the prior art. More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, the appended claims, and the accompanying drawing figures.